The present invention generally pertains to strip chart recorders and is particularly directed to programming a strip chart recorder so that it will operate unattended over a predetermined duration.
In a strip chart recorder a recording medium is advanced from a roll by a motor while a stylus produces a record on the recording medium of some variable that is being monitored, such as temperature, for example. The motor typically is either a synchronous motor or a stepper motor actuated in response to a signal from an oscillator. A stepper motor advances the recording medium by a predetermined distance upon each step of the motor, and thereby is preferred for moving the recording medium at a fixed rate of speed in a portable strip chart recorder which is battery-powered.
Portable strip chart recorders are often unattended for extended periods while in use. A typical application is for recording temperature variations in a refrigerated railway car over a period of several days.
A portable strip chart recorder has a capacity for containing a recording medium of a given length. With the motor advancing the recording medium at a fixed rate of speed, the portion of the recording medium that is used depends upon the duration of the recording. Thus a recording of a short duration is compressed into a small portion of the recording medium, with the remainder of the recording medium being unused. This compression of the recording reduces the resolution thereof, whereas if the complete length of the recording medium had been used the resolution would be greatly increased.